The TAC engineer added static routes and like you worked as a workaround but we did not want it that way and wanted it to learn it's route via eigrp so thats why we kept pressing the issue. After he changed the MTU and it worked this was his reasonin...

I wanted to see if you ever got your problem resolved. We experienced the same exact problem and after 2 hours with TAC we found the problem to be an MTU setting on the DS3 needed changing. On our remote site the serial interfaces all had an MTU of 1...